Two 5.0mm×5.0mm electrodes with a 0.10-mm-thick sheet of Mylar between them are

Question

Two 5.0mm×5.0mm electrodes with a 0.10-mm-thick sheet of Mylar between them are attached to a 9.0 V battery. Without disconnecting the battery, the Mylar is withdrawn. (Very small spacers keep the electrode separation unchanged.)

Part A

What is the charge before and after the Mylar is withdrawn?

Qbefore, Qafter =

Part B

What is the potential difference before and after the Mylar is withdrawn?

Vbefore, Vafter =

Qbefore, Qafter =

Part B

What is the potential difference before and after the Mylar is withdrawn?

Vbefore, Vafter =

Explanation / Answer

Remember and apply for parallel plate caapcitor, these as formulas

1. Capacitance C = K eoA/d   

where K is dieelctric constant ( for air K = 1)

k = 3.1 for mylar

eo is permnittivity constant = 8.85 e-12

A is area = pi^2 ( for circular plates) and l* b for rectanular plates

and

d is the distance between the plates

2.Charge Q = CV where V is potrntial difference

so after mylar was with drawn,

charge Qfinal = eoAV/d

Qf = (8.85*10^-12 * 5*10^-3*5*10^-3 * 9)/(0.1*10^-3)

Qf = 2*10^-11 C

before mylar was with drawn ,

Qintial = 3.1 * 2*10^-11 = 6.2*10^-11 C

]----------------------

Electric potential remains same before and after the mylar was with drawn

V before = V after = 9 V (ANSWER)

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